Here are some useful links.
Please add links to any other sites you find useful.

Second Life

http://secondlife.com
http://teen.secondlife.com
http://secondlife.com/community/education.php

Kids Connect

http://www.flickr.com/photos/kidsconnect/
http://zoomlab.org
http://zoomlab.org/wiki/index.php?title=Kids_Connect
http://danwinckler.com/blog/archives/2006/08/23/gems_from_kids_connect/ - see video clips the kids made

SimTeach: Information for educators using Multi-User Virtual Environments such as Second Life
http://www.simteach.com/

Global Kids: online leadership program in SL

http://www.globalkids.org/AboutGK/PressCoverage/03282006.jsp
http://www.holymeatballs.org/second_life/holy_meatballs_of_divine_spongiform/

Snapzilla: Pictures taken by teenagers of the Teen Grid
http://www.sluniverse.com/pics/snapshots.aspx?type=teen

Machinima: A guide to creating machinima films in Second Life

Useful stuff

How to present in SL (by Global Kids)
Talks and presentations from the New Media Consortium (NMC) conference in 2006
Talks and presentations from the Serious Games Summit
Video by ABC News about Second Life